linux - TCP socket performance

06
2014-04
  • Questioner

    There are three Linux Debian machines connected via Gigabit Ethernet router:

    1. Server machine A that is the source or HTTP streaming traffic with bandwidth 300 KBps.
    2. Proxy machine B that connected to server machine A and perform several calculations and bypass sligtly modified traffic to its clients. All these operations are performed by one application in one thread with use of libevent.
    3. Client machine C that is connected to proxy machine B with 32 curl clients. So proxy machine B handle all connections (1 AB connection and 32 BC connections) in one thread.

    There is an issue exist. HTTP traffic between machines A and B stuck regularly for one half to several seconds. Symptoms:

    1. According to netstat the Send-Q of machine A does not change on stuck reprodution.
    2. According to IOCTL(FIONREAD) there are no bytes in input queue for application on proxy machine B.
    3. According to tcpdump and wireshark (tcpdumps from both machines A and B) I see TCP Retransmission on both machines A and B and TCP Dup ACK on machine B only.

    It is may be significant: all three machines are servers machines. According to iftop and htop there is a big room in CPU, memory and network utilization.

    My question is how can I improve the perfomance of the connection AB?

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  • lathomas64

    How can I force all currently open sockets in linux to close from the command line?


    • Related Answers
  • cYrus

    Maybe it's easier to shut down a specific interface, for example:

    # ifconfig eth0 down
  • someguy

    to flush all your rules in the filter table iptables -F
    set default behavior to drop in INPUT chain iptables -P INPUT DROP

    at this point all local sockets should be unavailable to a remote host if you have a redhat based os you should also use iptables -X to get rid of their custom chain for INPUT

    if you want to the rules to remain on startup then you need to either include these in a script that runs in the /etc/rc.local file or use iptables save

    This is all assuming that what you said you want to do is what you want to do.